دانلود رایگان مقاله اثربخشی لایه های مختلف قلیایی پراکنده برای قبل از زهکشی معدن اسیدی آهن دار

abstract

Dispersed alkaline substrates (DAS) have been successfully used in passive treatment of highly contaminated acid mine drainage (AMD) to limit coating and clogging issues. However, further optimization of DAS systems is still needed, especially for their long-term efficiency during the treatment of ferriferous AMD. In the present study, three types of DAS comprised of natural alkaline materials (wood ash, calcite, dolomite), in different proportions (20%v/v, 50%v/v, 80%v/v), and a substrate with high surface area (wood chips) were tested in 9 batch reactors. The testing was carried out, in duplicate, for a period of 91 days, to evaluate the comparative performance of the mixtures for iron pre-treatment in ferriferous AMD (2500 mg/L Fe, at pH 4). Results showed increasing of pH (between 4.15 and 7.12), regardless of the proportion of alkaline materials in the DAS mixtures. Among the tested mixtures, wood ash type DAS were more effective for Fe removal (99.9%) than calcite or dolomite type DAS (up to 66%). All tested DAS had limited efficiency for sulfate removal and an additional treatment unit, such as a sulfate-reducing biochemical reactor, is needed. Moreover, due to the similar performances of the calcite and dolomite DAS, they could be potentially substituted and rather be used in a polishing treatment unit. Based on these findings, the most promising mixture was the 50% wood ash type DAS (WA50-DAS).

4. Conclusion

The present study evaluated three types of DAS (dispersed alkalinity substrate), comprised of natural alkaline materials (wood ash, calcite, dolomite) in different proportions (20% v/v, 50% v/v, 80% v/v), and substrate with high surface area (wood chips) in 9 batch reactors, for Fe pre-treatment in ferriferous AMD (>1500 mg/ L Fe), over a 91-day period. Among the tested DAS, the one composed of wood ashes (WA) was the most effective (99.9%), whereas those containing calcite or dolomite gave comparable performance. A contact time of 6e11 h was required for Fe concentrations to be decreased to below 500 mg/L. The efficiency of the WA-DAS systems was similar, regardless of the proportion of wood ash. However, the possible washing out/clogging because of the high content of fine particles of W80, as well as the rapid alkalinity depletion of WA20, that eventually lead to limited long term performance, pointed out WA50 as the best choice for Fe pretreatment. In a very short term run, calcite-DAS was more effi- cient (66%) than dolomite-DAS (22%). However, in a mid-term, calcite- and dolomite-DAS could be potentially substituted and used in a polishing unit for the passive treatment of iron-rich AMD. All DAS mixtures showed Al, Zn and Pb removal, except for Mn, which was removed up to 50% only in WA50. SO4 2
removal in WADAS was higher (18e40%) compared to calcite- or dolomite-DAS (<10%). Nonetheless, additional treatment units for sulfate removal are necessary.